Isotope Chronostratigraphy of OCS Well South Timbalier Block 198, Northwestern Gulf of Mexico

Dwight M. Trainor, Douglas F. Williams

Isotope chronostratigraphy is a modern technique for deriving a high-resolution geochronology for sediments of the outer continental shelf (OCS)-slope of the western Gulf of Mexico. The release of proprietary stable isotope data from OCS exploration well South Timbalier Block 198 enables the first public presentation of specific isotopic data compared to previously established global and regional composite isotope records. The oxygen isotope type records for the Pliocene-Pleistocene for both the global oceans and western Gulf of Mexico are based on deep-sea cores and numerous exploration wells. The type record shown for the western Gulf of Mexico is a revised composite record defining 133 oxygen isotope stages from 0 to 4 m.y. This regional type record is directly compara le to the global composite isotope record.

The oxygen isotope record for the well was derived utilizing two different foraminiferal species. The isotopic composition of the planktonic foraminifera Globigerinoides ruber was used in the upper 8,000 ft of the well. The benthic foraminifera Uvigerina was examined in the lower 5,000 ft where G. ruber was not present. This combined oxygen isotope record for the well, when integrated with the available biostratigraphy, enabled the recognition of 47 isotope stages of the Pliocene-Pleistocene section of the well and an additional series of glacial-interglacial cycles in the late Miocene. The isotope chronostratigraphy enabled the recognition of two hiatuses spanning the time interval from ^dgr¹⁸O stage 93 at 2.76 Ma and from ^dgr¹⁸O stage 131 at 3.9 Ma to the late Miocene at approximately 5 Ma. This high-resolution geochronology for OCS well South Timbalier Block 198 provides detailed information on sedimentation accumulation rates in this area.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.